This invention relates in general to hydrogen purification by which is meant an improved process for the removal of gaseous impurities from an impure gas stream of hydrogen contaminated with carbon monoxide, and with one or more additional impurities. The additional impurities can be carbon dioxide, oxygen, nitrogen, water, and/or methane. Methane is frequently present in commercially available impure hydrogen at a level of 5 parts per million (ppm) which is 5,000 parts per billion (ppb). Methane can also be formed in situ by the reaction of the hydrogen with the carbon monoxide and or carbon dioxide. Methane formation is avoided in this new improved process. This process can be employed to purify impure hydrogen such that the resultant purified gas contains less than 50 ppb or even less than 20 ppb of methane i.e. less than 20 parts by volume of methane per 1,000,000,000 parts by volume of hydrogen.
The semiconductor industry is developing integrated circuits with ever more increasing line densities requiring that the materials used in the manufacturing process be of ever increasing purity. As hydrogen is one of the gases used in these processes, it must be as pure as possible. The impurities present in commercially available hydrogen include: carbon monoxide, and one or more additional impurities. The additional impurities can be carbon dioxide, oxygen, nitrogen, water, and/or methane.
One prior method for the purification of impure hydrogen is the selective diffusion of hydrogen through palladium or palladium alloys as described for example in U.S. Pat. No. 3,534,531. Such processes suffers from a number of disadvantages. Unfortunately the rate of diffusion increases with the pressure drop across the sides of the palladium barrier. Another disadvantage is the requirement for a high operating temperature in order to achieve an economical throughput. Furthermore, as the impurities are blocked by the palladium barrier, a removal device must be provided. Such a removal device is described in U.S. Pat. No. 3,368,329. Removal devices are expensive to acquire and costly to maintain. Another disadvantage is the propensity of the palladium barrier to rupture with consequent leakage of impurities into the purified gas stream. This propensity is all the more prevalent because of the incentive to make the palladium barrier thin and to increase the differential pressure in order to increase the throughput. The use of high-temperature, high-pressure hydrogen is dangerous because of its propensity to explosively, exothermically combine with atmospheric oxygen. Finally palladium is expensive.
Accordingly it is an object of the present invention to provide an improved process for the purification of impure hydrogen substantially free of one or more of the disadvantages of prior process for the purification of impure hydrogens.
Another object is to provide an improved process for the purification of impure hydrogen which does not require the use of either palladium or its alloys or its compounds.
Another object is to provide an improved process for the purification of impure hydrogen which does not require the use of a diffusion membrane.
Another object is to provide an improved process for the purification of impure hydrogen which does not require the heating of the impure hydrogen.
Another object is to provide an improved process for the purification of impure hydrogen which does not require the use of hydrogen under pressure.
Another object is to provide an improved process for the purification of impure hydrogen which avoids the production of methane by the reaction of the hydrogen with either the carbon monoxide or the carbon dioxide which is present.